1. Field of the Invention
The invention relates to valves, and more specifically, to a dual-action vent check valve which prevents elevated fluids from passing through the valve in either of two opposed directions. The invention is particularly adapted for use with vents for sewer out-fall lines.
2. Description of the Prior Art
Underground enclosures, such as sewer manhole structures, vaults for underground utilities, underground storage tanks, underground piping systems, and the like, often include vents for permitting air and other gases to flow between the enclosures and the surrounding atmosphere. Such vents permit gas pressure to equalize between the enclosures and the atmosphere, and permit off-gases to vent from the enclosures to the atmosphere. These vents may include a vertical vent pipe having a substantially open end. In flood prone areas, the upper ends of such vent pipes may be elevated above a predetermined flood level to prevent the inflow of floodwater into the enclosures through the open vents during flood conditions. The top ends of such vent pipes may include a down-turned “gooseneck” portion to inhibit the entry of rainwater or other materials into the otherwise open end of the vent pipe.
As an alternative to elevated vent pipes, an entire manhole structure may be elevated above a predetermined flood level to prevent inflows of floodwater. Concrete risers may be stacked to a desired elevation to elevate the manhole above flood level. Though such elevated vent pipes and manholes are at least somewhat effective to prevent floodwater entry, they add considerable cost to the construction of underground installations. Furthermore, such elevated structures are visually prominent and may be unsightly, particularly in residential areas.
In order to eliminate the need for such elevated structures in flood-prone areas, inverted vent check valves are sometimes mounted on the down-turned ends of vent pipes to prevent inflows of floodwater through the vents. Such valves include a single internal float which closes the valve in response to rising floodwater. Though such single-action vent check valves are effective to prevent floodwater from entering underground installations, such valves cannot prevent rising liquids inside the underground structures from flowing from the structures through the vents. In the case of sewer out-fall lines, rising liquids in an over-capacity sewer may rise in the vent pipe and pass out of the sewer system through the vent pipe. Such sewer outflows are undesirable because they may contaminate the surrounding area and waterways, thereby creating a potential health hazard and possibly harming the environment. Therefore, there is a need for a dual-action vent check valve which not only prevents inflows of floodwater, but which also prevents outflows of liquids from vented underground structures. In particular, there is a need for a dual-action vent check valve suited for installation on vents for sewer out-fall lines in flood prone areas.
In the case of sewer vents, sewer off-gases may be vented from the sewer to the surrounding atmosphere through the vents. Because such gases may have an objectionable or offensive odor, such vented gases are undesirable, particularly in residential areas. Therefore, there is also a need for a means to neutralize objectionable odors from sewer vents. Further, there is a need for a dual-action vent check valve which neutralizes objectionable odors vented from sewers through the valve.